Tom Tugendhat speaks on a fact-finding trip of the foreign affairs select committee to Armagh and Belfast.
Photograph: Niall Carson/PA

The consequences of Britain crashing out of the EU without a deal would be “extremely serious” for Northern Ireland, Tom Tugendhat, the chair of the foreign affairs select committee, has warned.

The committee heard concerns from people in Armagh and Belfast about a return to violence, the threat to harmonious relations on the border and anger that the Stormont assembly was still not up and running, 28 months after power sharing collapsed in the region.

A charity director who works with primary schools in deprived areas of Belfast said it was “unconscionable” that teachers and the police had to wait months for pay to be signed off because the local assembly institutions were not running.

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Another local community representative claimed 90% of Westminster politicians were “ignorant” about the region and were not qualified to make decisions about the Irish border.

Speaking on the fact-finding trip, Tugendhat, the Conservative MP for Tonbridge and Malling, said: “Many of the things we already knew were made much clearer. The centrality of having to consider this part of the UK in particular because of the border with the EU is sadly too often overlooked in Westminster.”

He was speaking after members of the committee met local community groups to discuss the impact of Brexit.

“The consequence of no deal in Northern Ireland is extremely serious. The truth is no deal is not sustainable,” said Tugendhat.

“Failure to agree a deal between the UK and our most important trading partner, the EU, [is] not a sustainable state unless we are bidding to be Mauritania.”

Peter Bunting, a former leader of the Irish Congress of Trade Unions, was blunter about Tugendhat’s Westminster colleagues. “There seems to be widespread ignorance of the facts,” he said.

He said the problem with the select committee members in the delegation was that they were all remainers – Tory Brexiters such as the former cabinet minister Priti Patel were not on the trip despite being part of the committee.

“These are the people who do not seem to learn about the vagaries of Northern Ireland, these are the people who are making decisions,” Bunting said.

“I would say 90% of parliamentarians in Westminster are totally ignorant of what’s good for Northern Ireland.”

Several representatives who met the committee warned how the domino effect of Brexit uncertainty in Northern Ireland was different to the rest of the UK.

Sean Feenan of Community Foundation, a cross-border project aimed at building peace, said Brexit was pushing communities into hardened “green” and “orange” positions, a reference to nationalism and unionism, and this was being exploited by some. “Part of our concern is what is the propensity for violence,” he said.

Feenan, among others, said Westminster needed to wake up to reality in Northern Ireland, with the census in 2021 widely expected to show the number of people of Catholic heritage outstripping those of Protestant heritage for the first time.

This could feed into demands for a border poll and foster more uncertainty. “The concern is that there are groups that will use any excuse to raise tension and anxiety, and this could lead us to violence,” he said.

Ray Hayden, one of the founders of Goliath Trust, a charity providing for vulnerable children in deprived areas “blighted by paramilitaries”, said “there was a lot of frustration and concern expressed” in the private meeting with the committee about the failure to restore power sharing.